The present invention relates to stretchable circuit boards including a stretchable base and a stretchable wiring portion, and methods for manufacturing the same.
In the wearable device market and the medical device market, biological sensors and biological information monitors have received much attention in recent years. For example, the sports industry has been making an effort to quantify body movements of competitors in a highly precise manner in order to improve competitors' physical ability or skills. In such a case, wearable biological sensors that sense movement of a living body are used in some occasions. In addition, the medical industry has been trying to detect vital signs (biological information) such as electrocardiograms, heart rates, blood pressures, and body temperatures for the purpose of treatment of diseases or taking measures against presymptomatic diseases. In such a case, biological information monitors that sense biological information may be used. In general, these biological sensors or biological information monitors are attached to garments or equipment, and these garments or equipment are worn to perform sensing or monitoring.
However, as a human body moves, these garments or equipment are slightly misaligned from a body. This causes a problem of misalignment of the biological sensor or the biological information monitor from the targeted portion of a living body, resulting in significant deterioration in sensing accuracy or monitoring accuracy.
The problem described above can be prevented if the biological sensor or the biological information monitor is attached directly onto the human body. Thus, in recent years, studies have been made as to a technique called stretchable electronics having a base or wiring that can stretch in in-plane directions, and circuit boards that can stretch in association with movement of joints and the like of a human body are proposed. In a case where biological sensors or biological information monitors are used in medical application or the like, it is desired that at least a portion of the biological sensors that is in contact with a living body or used in the vicinity of the living body should be disposable from the viewpoint of prevention of infectious diseases.
A stretchable circuit board of this type includes a circuit board described in Japanese Patent Application Laid-open No. 2014-236103. This circuit board includes a stretchable base and an electroconductive pattern containing electroconductive microparticles and elastomer, and the entire substrate of this circuit board has stretchability. Furthermore, Japanese Patent Application Laid-open No. 2014-162124 describes a stretchable circuit board, in which an island composed of a material having Young's modulus higher than that of a stretchable base is formed into a thin membrane through a printing method, and is embedded in the base. This island has elements mounted thereon, and individual islands are connected by stretchable wires. This document describes that, with this configuration, it is possible to prevent elements from breaking or prevent breakage of wires extending over a boundary between the island and the base.